The present invention relates to a method and apparatus for cleaning an image carrier that is used for transferring a toner image onto a recording medium, wherein a black image, i.e., an image, the entire area of which is filled with toner, is formed on the image carrier and is transferred onto a cleaner that engages the image carrier for removing dust therefrom.
The invention is applicable, for example, to electrographic or magnetographic copiers and printers, and, more generally, to all kinds of image forming apparatus in which a toner image is transferred from an image carrier onto a recording medium.
It is a general problem with such image forming apparatus that certain types of recording media, especially certain types of paper, such as offset paper, home-cut paper that has been cut into sheets in a special apparatus on the premises of the user, and the like, tend to release a considerable amount of dust inside the apparatus. The dust is deposited on sensitive component parts of the apparatus and disturbs the image forming process. Among other contaminates, dust is deposited on the image carrier, so that the image carrier has to be cleaned from time to time.
U.S. Pat. No. 5,227,844 discloses a cleaning process in which a specific cleaning sheet is fed through the apparatus in place of the regular recording medium in order to collect and remove the dust.
A cleaning process as defined above has been employed by the applicant. In this process, a cleaner, typically in the form of a drum, e.g., a so-called spiral cleaner, is arranged at the periphery of the drum-type or belt-type image carrier, so as to remove the dust from the surface of the image carrier and to collect the dust on the cleaner. However, with an increasing amount of dust being deposited on the cleaner, the cleaning capacity degrades, so that the dust can no longer be removed completely from the image carrier. For this reason, the cleaner has to be regenerated from time to time. This is achieved by means of a so-called black image process in which a black image is formed on the image carrier and is then transferred onto the cleaner. As a consequence, the dust that has been deposited on the cleaner is buried in a layer of toner, and this restores the capacity of the cleaner to collect more dust. The term “black image” is used for simplicity and is to indicate that the entire surface of the image carrier that is normally used for carrying an image is covered with a continuous layer of toner, but it will be understood that the actual color of the toner (normally black) is not important.